Vegetation and Soils of Shell Middens on the Coast of British Columbia

Abstract

Six vegetation dominance types were recognized on 23 shell middens. Combinations of the dominants Alnus rubra Bong., Acer macrophyllum Pursh, Gaultheria shallon Pursh, Mnium insigne Mitt., Picea sitchensis (Bong.) Carr., Poa trivialis L., Polystichum munitum (Kaulf.) Presl., Pseudotsuga menziesii (Mirbel) Franco, Rhytidiadelphus triquetrus (Hedw.) Warnst., Rubus spectabilis Pursh, Tellima grandiflora (Pursh) Dougl., Thuja plicata Donn, Tsuga heterophylla (Raf.) Sarg., and Urtica dioica var lyalli (Wats.) C.L. Hitchc. characterize each vegetation type. A chart is included for rapid field identification. The major factors influencing vegetation variation are probably moisture regime and logging disturbance. Apart from lower concentrations of total nitrogen in midden horizons of Tsuga—dominated stands, no significant relationships are apparent between vegetation type or individual dominants and midden age since occupation, soil pH, soil particle—size ratio, organic carbon, total nitrogen, carbon—to—nitrogen ratio, exchangeable calcium, or available phosphorus. Midden horizons contain large quantities of mollusc shell, often with ash and other cultural detritus, and have high levels of exchangeable calcium (5,125—14,350 ppm) and high pH (6.9—7.2). Vegetation on adjacent areas with comparable topography is frequently similar to midden vegetation; thus shell deposits appear to have little influence on composition and structure of forest communities in this area. Radiocarbon age estimates of upper shell deposits in 13 middens ranged from 770 ± 90 to 6,250 ± 110 years B.P. (before 1950). Organic carbon, total nitrogen, and exchangeable calcium values apparently decrease with increasing bidden age. Further study is required to facilitate the development of a fast, inexpensive method for approximate dating of bidden deposits.